I can't make sense of anything. My head's in a panic and I can't get my thoughts straight.
Literal
What [subject-が] what [wonder-だか] not-understand. Head [subject-が] panic [to-に] fallen can't-organize.
何がなんだか分からない is a set expression for total bewilderment — 'I can't tell what's what.' パニックに陥る ('to fall into panic') uses 陥る, a more dramatic verb than なる for entering a negative state. 整理がつかない ('can't get organized') applies the physical concept of sorting/organizing to mental processes.